The present invention relates to a power supply apparatus having a function of compensating for changes in voltage.
With advances of scientific technology, the degree of dependence on an a.c. power source has been increased. Correspondingly, the a.c. power source has been stably supplied. In particular, the setting of transmission lines to a plurality of lines or circuits and the cutting off of the a.c. power source at high speed can bring about advantageous effects. It is therefore very rare to stop the supply of power.
However, when a thunderbolt or the like falls even if such protection is made, the a.c. power source greatly varies although its variation happens in a moment. Occasionally, the a.c. power source is cut off. Commercially-available devices are not affected by an instantaneous variation in the a.c. supply. However, devices are also known which are affected by the instantaneous variation in the a.c. supply. As such devices, there are known complex electrical facilities such as a semiconductor manufacturing device, etc. Therefore, the instantaneous variation in the voltage causes the stop of operations of the electrical equipment and becomes a factor that impedes production. To avoid this, a so-called power supply apparatus having a function of compensating for changes in voltage is now used wherein a power source capable of supplying power at all times is separately provided and when the a.c. power source varies in voltage, a desired voltage is supplied so as to compensate for its variation.
A typical example of this type of power supply apparatus will now be described. One terminal supplied with an input from an a.c. power source is electrically connected to one of output terminals via the primary winding of a transformer. Incidentally, the connection of the secondary winding of the transformer will be described later. In conjunction with this, the voltage supplied from the a.c. power source is rectified by a rectifier and is then stored in a capacitor. When a malfunction of the a.c. power source is detected, the voltage stored in the capacitor is converted to an alternating current by an invertor. Further, the invertor is electrically connected to the secondary winding of the transformer which couples the input terminal and the output terminal to each other. Namely, when the anomaly of the a.c. power source is detected, the voltage stored in the capacitor is supplied to the output terminal through the secondary winding of the transformer and the primary winding thereof coupling the input terminal and the output terminal to one another (first prior art).
Further, another typical example of the power supply apparatus will be described below. A voltage supplied from an a.c. power source is transformed by a transformer and is rectified by a rectifier. The rectified current is normally converted into an alternating current by an invertor so as to be supplied to an output terminal. With this, the voltage rectified by the rectifier is stored in a capacitor. When the a.c. power source now malfunctions, the voltage stored in the capacitor is converted into the alternating current by the invertor and is supplied to the corresponding output terminal (second prior art).
These compensating circuits are normally accommodated in a rack. Further, legs are mounted to the rack so that the rack is held on the ground with the legs interposed therebetween. The legs have been conventionally fixed to the rack.
Further, a certain kind of rack is required to be able to move. In this case, casters are mounted to the rack, which is held by rolling friction between the ground and the casters. The casters have been conventionally fixed to the rack.
In the first prior art, the input terminal supplied with the input from the a.c. power source is electrically connected to the output terminal via the winding of the transformer. Since a current produced from the a.c. power source normally passes through the transformer, the transformer will result in an increase in size if it is designed so as to bear the current. Therefore, the compensating circuit becomes large in size as a whole and becomes expensive.
In the second prior art, the alternating current is converted into the direct current, which is then converted into the alternating current to thereby obtain a compensating supply. Therefore, the transformer produces much losses due to such conversion and is hence unable to bear the practical use. Further, the transformer becomes complex in structure and expensive.
A first object of the present invention is to provide a power supply apparatus having a function of compensating for changes in voltage, which makes it unnecessary to use a large transformer and is reduced in size and cost.
In the prior art, for example, a human being checks the state of an output of an a.c. power source and confirms that the a.c. power source has been returned to a normal or proper state. Thereafter, a compensating source is reset to the a.c. power source. Therefore, the time required to reset the compensating source to the a.c. power source becomes relatively long. If the voltage is supplied from the compensating source for such a long time, the compensating source will result in an increase in size and cost.
A second object of the present invention is to provide a power supply apparatus having a function of compensating for changes in voltage, which is capable of holding a compensating source in a small size and being reduced in whole size and cost.
In the prior art, when a voltage produced from an a.c. power source becomes lower than a predetermined value, the a.c. power source is changed over to a compensating source. On the other hand, when the voltage of the a.c. power source becomes higher than the predetermined value, the compensating source is reset to the a.c. power source.
When the voltage produced from the a.c. power source is repeatedly raised and lowered within a relatively short time due to some reasons, the a.c. power source is often changed over to the compensating source in the case of such a construction. As a result, a transient state is produced each time the a.c. power source is changed over to the compensating source, thereby causing a problem.
A third object of the present invention is to provide a power supply apparatus having a function of compensating for changes in voltage, which is capable of bearing a variation in an a.c. power source even if such a variation is repeated within a short time.
Further, in the prior art, the value of a voltage employed in the prior art is compared with a predetermined value. Based on the result of comparison, detection is made as to whether the a.c. power source malfunctions. When such a simple comparison is made, it is difficult to virtually avoid errors in detection. Even though the a.c. power source is not brought into an abnormal or improper state, the a.c. power source is changed over to the compensating source. Further, even though the a.c. power source is brought into the improper state, the a.c. power source is not changed over to the compensating source, thereby stopping the supply of power.
A fourth object of the present invention is to provide a power supply apparatus having a function of compensating for changes in voltage, which is capable of accurately detecting an improper state and accurately changing an a.c. power source to a compensating source when the a.c. power source is brought into an improper state.
A compensating circuit is generally accommodated in a rack and legs are mounted to the rack so as to hold the rack on the ground. Since, however, the legs are fixed to the rack in the prior art, these legs will cause inconvenience when the entire apparatus is to be accommodated within a slight space, for example. When it is necessary to devise the way of disposing the apparatus, these legs will cause inconvenience when the apparatus should be changed from a vertically-disposed state to a horizontally-disposed state, for example.
A fifth object of the present invention is to provide a power supply apparatus having a function of compensating for changes in voltage, which has flexibility to the provision of the entire apparatus.
Further, in some kind of compensating circuit, casters are mounted to a rack to move the rack in such a manner that the rack is held by rolling friction between the ground and the casters. Since, however, the casters are fixed to the rack in the prior art, it is needless to say that the rack must be shifted so as to avoid an object relatively large in height, for example, thus causing inconvenience upon movement of the rack.
A sixth object of the present invention is to provide a power supply apparatus having a function of compensating for changes in voltage, which is able to easily move.